Modern hearing aid fitting software provides a clinician with a display of response curve associated with the gain of a hearing assistance device. A clinician uses the fitting software to adjust the gain and other settings of the hearing assistance device so that the hearing assistance device's output in the wearer's ear matches a prescribed target. However, the fitting software lacks the ability to quickly compare changes in the gain response curve across multiple fitting sessions. Accordingly, there is a need in the art for apparatus and methods to provide improved visualization of changes in gain response curves over time.